The present invention relates to a nasal mask. Known nasal masks of which the applicant is aware have suffered from various disadvantages. For example, known nasal masks do not prevent leakage of gas such as air or oxygen from the mask efficiently, and do not distribute forces evenly on the face of the user. With known masks, an undesirably high tensile force has to be exerted by the straps or other mask retaining devices that hold the mask to the user""s head, and as a result excessive pressure tends to be exerted on the user""s face, causing breakdown of the skin, for example, on the bridge of the nose. Further, known masks interfere with use of eye glasses while wearing the mask, and may present the difficulty that a gas tube may become pinched or obstructed when the user lies on one side, for example when the user is sleeping.
Another disadvantage of known masks is the build-up of exhaled CO2 within the mask and the patient""s mouth and airway due to an inadequate ventilation of exhaled air. This build-up is sometime referred to as xe2x80x9cdead spacexe2x80x9d. With known masks, it has been necessary to make a design trade off between providing a sealed environment for inhalation and providing a resistance-free path for exhalation with minimal dead space.
It would be advantageous to provide a nasal mask that provides both a sealed environment for inhalation and reduced resistance to exhalation with minimized dead space.
The present invention provides a shell portion and an interface member for a nasal mask comprising a shell portion defining a hollow enclosure with a rearwardly facing opening defined by edge portions of the shell portion, and a resiliently deformable endless interface member engaging with and extending around said edge portion of the opening and adapted to form a seal between the shell portion and the user""s face, and wherein the shell portion and the interface member are at least generally symmetrical about a median plane, and said shell portion has two gas inlet orifices disposed one on each side of the median plane. With this arrangement, the mask may be supplied with gas through two relatively small diameter flexible tubes coupled to the orifices, respectively. The small diameter tubes exert only relatively small tensile forces away from the user""s face, and therefore only relatively small forces need to be exerted by retaining straps to retain the mask, and as a result, excessive application of force to the user""s face and problems such as breakdown of skin on the bridge of the nose can be avoided. Further, the smaller tubes can be easily oriented in any desired position relative to the mask. For example, they may be positioned downwardly below the mask to facilitate wearing of eye glasses, or may be positioned centrally of the top of the user""s head so that they are not obstructed if the user lies on one side.
In a preferred form, the gas inlet orifices are positioned symmetrically with respect to the median plane, and the inner side of the shell adjacent each orifice is provided with an inwardly extending tubular portion for engaging deformable nasal pillows that may form a seal between each orifice and a nostril of the user.
In one aspect, the present invention provides a nasal mask for use by a patient, the nasal mask including a shell portion, the shell portion being in sealed communication with the patient""s face and having one or more inlet orifices for receiving supplied gas, the shell portion having an exhalation orifice and, adjacent the exhalation orifice, an outwardly extending tubular formation defining a flow passage through the exhalation orifice; and a balloon exhalation valve removably connected to the outwardly extending tubular formation, the balloon exhalation valve having a balloon adapted to controllably seal and unseal the flow passage.
In another aspect, the present invention provides, in combination, a nasal mask and a balloon exhalation valve, the nasal mask including a shell portion, the shell portion defining a hollow enclosure with a rearwardly facing opening defined by edge portions of the shell portion, and wherein the shell portion is at least generally symmetrical about a median plane, the shell portion having two gas inlet orifices disposed one on each side of the median plane, the front of the shell portion having an exhalation orifice approximately centred on the median plane and, adjacent the exhalation orifice, an outwardly extending tubular elbow formation defining a flow passage through the exhalation orifice, the balloon exhalation valve including a hollow tubular casing having a lower end face with a central passage therethrough, an inlet tube securely attached to the lower end face of the casing and passing through the central passage, and a balloon disposed within the casing, the mouth of the balloon being in sealed communication with the inlet tube, wherein the upper end of the casing is removably connected to the outwardly extending tubular elbow formation, and wherein the casing has an outlet orifice disposed proximate the outwardly extending tubular elbow, the outlet orifice defining a flow passage from said exhalation orifice through the casing, and wherein the balloon seals the exhalation orifice when the balloon is inflated.
Preferred embodiments of the present invention will now be described in more detail, by way of example only, with reference to the accompanying drawings.